Atomizer assembly for a flame spectrophotometer



July 10, 1956 K. w. GARDINER 2,753,753

ATOMIZER ASSEMBLY FOR A FLAMBSPECTROPHO TOMETER Filed March 19, 1955INVENTOR. KENNETH W. GARDINER MkaM ATTORNEYS United States PatentATOMIZER ASSEMBLY FOR A FLAME SPECTROPHOTOMETER Kenneth W. Gardiner,Watertown, Mass. Application March 19, 1953, Serial N0. 343,348

4 Claims. (CI. 88-44) The accuracy of flame spectrophotometers, as usedin making quantitative determinations of extremely small quantities ofelements dissolved or dispersed in a given sample, is primarilydependent on the light measuring instrumentalities and the operation ofthe atomizer-burner assembly. Recent developments in photoelectriclightmeasuring devices provide exceptionally good lighbdispersing andintensity measuring means, as will appear more fully with reference tosuch literature as Bulletin 1675 of the National Technical Laboratories;but the available atomizer-burner assemblies present serious problems inthat they lack the necessary stability in operation to achieve thedesired precision and accuracy; the volume of sample required per minuteof atomization is objectionably high, being of the order of 2 ml. perminute; the difiiculty in accurately controlling the rate ofatomization; and the time and dilficulty involved in clearing theatomizer assembly or changing samples.

The principal object of the present invention is to provide an atomizerassembly which is of simple design, reliable and efiicient in operationand which overcomes the aforementioned difliculties of prior assemblies.

Further objects relate to features of construction and operation andwill be apparent from a consideration of the following description andthe accompanying drawings, wherein:

Fig. 1 is a perspective view of the end portion of a flamespectrophotometer and associated burner-atomizer assemblies constructedin accordance with the present invention;

Fig. 2 is an enlarged vertical section through the burner and atomizerassembly;

Fig. 3 is a section on the line 3-3 of Fig. 2; and

Fig. 4 is a section on the line 4-4 of Fig. 2.

The embodiment herein shown for the purpose of illustration comprises aspectrophotometer P, such for example as a Beckman, one end of which isprovided with a light slit S below which is a braket or shelf 1 for theburner assembly B and a clamp 2 for the atomizer as sembly A. Above theburner B is a chimney C for conducting the hot gases away from theapparatus.

The burner B may be of any conventional design but is here shown ascomprising a cylindrical metal casing 4 surrounded by a cooling coil 5and having a gaseous fuel inlet 6. Within the casing 4 is a plurality ofvertical tubes 8 extending from the bottom wall of the casing upwardlyto its top wall 10 which is formed with a plurality of small ports 11disposed about the discharge ends of the tubes 8, as shown in Fig. 2.

The atomizer assembly A is preferably of glass, plastic, stainless steelor other suitable material and comprises a cylindrical atomizing chamber15, the upper end of which is preferably of generally conical shape todefine a restricted outlet 16, and the lower end of the chamber ispreferably open to communicate with a cup-like samplereceiving container18 supported on a block 20 or other means which holds it about the lowerend of the chamber, as illustrated in Figs. 1 and 2. A pressure tube 22,

through which oxygen or air passes, extends through the side wall of thechamber and its inner end is tapered to provide a nozzle 24 whichprojects upwardly in approximate vertical alignment with the outlet 16.The inner end portion of the tube 22 is integrally joined to a liquiddelivery tube 25, the lower end of which extends to the bottom of thechamber to receive liquid in the container 18. The upper end of the tube25 is in the form of a tapered are 26 the end of which is contiguous tothe nozzle 22 so as to provide an atomizer.

Integral with the upper end of the atomizer chamber 15 is a cylindricalreflux chamber 30 the lower end of which preferably is generally conicalso as to define an inlet 31 communicating directly with the outlet 16 ofthe atomizing chamber. The upper end of the reflux chamher is open toreceive a removable cap or closure 34 formed with an off set openingwhich receives a delivery tube 35. The upper part of the delivery tube35 is flared outwardly as indicated at 36 and extends upwardly throughan opening 38 in the shelf 1 so as to communicate directly with thelower ends of tubes 8 of the burner assembly B.

A reflux member or baffle all is concentrically supported within thechamber 30 by an integral stem 41, the upper end of which is securedwithin an opening in the cap 34. The baffle 40 is of concave-convexshape with its concave surface facing downwardly and its peripheryspaced from the convergent chamber wall so as to define an an nularpassage 42 (Fig. 3) between the inlet 31 and delivery tube 35.

In operation the atomizer assembly A, without the container 18, is firstclamped in place as shown in Fig. 1, after which the container 18 withthe sample to be tested is fitted about the lower end of the chamber andthe block 20 is then positioned to support the container in place. Wateris admitted to the cooling coil 5 and hydrogen, propane or othersuitable gas or a mixture of gases is admitted to the burner B throughone or more inlets 6. The gas is then lighted and the flame adjusted,after which low pressure air or oxygen is admitted through the inlettube 22 and is adjusted to give the desired spray which is directedupwardly toward outlet 16. The spray discharged through outlet 16comprises a mixture of relatively large droplets in a body of mist whichstrikes the reflux or bathe 40 in passing into the chamber 30.Condensate and large droplets accumulating on the baflle and the innerwall of the chamber are returned by gravity into the chamber 15 and flowback into container 18; but the fine mist or smoke which passes throughthe passage 42 into the upper part of the chamber 349 is carried throughthe delivery tube 35 and discharge into the tubes 3 of the burner B. Themist discharged by the tube 8 mixes with the jets of gaseous fuelpassing through the openings 11 and there is produced a broad uniformflame, the hot portion of which is aligned with slit S, thus allowingmeasurement in the region of maximum spectral emission line intensity.

It usually requires but a matter of minutes to complete the analysis,but in event more time and sample were required, the container 18 may beremoved and replaced with an additional sample in a short time. Afterhaving the completed analysis, the assembly A, including container 18,may be flushed out, after which the operation may be repeated in testinganother sample.

An outstanding feature of the invention is that the atomizer assemblyoperates at a maximum eficiency with an applied air pressure of onlythree pounds per square inch or less, in comparison to the normalworking pressure of 15 to 25 pounds per square inch required in othertypes of vaporizing systems. I have found that a low working pressureresults in a much slower passage of air or oxygen carrying the vaporizedsample into the flame,

and as acons'equence the flame has much less turbulence and-flicker,which is of particular importance when working at low light levelsand-where small differences in emitted light intensity are beingmeasured. Moreover, my assembly exhibits an 'optimumin applied Workingpressure above which efii'ciency and consequent emitted-light intensitybecome practically 'independent of those pressure fluctuations whichnormally introducesizable errors.

Asthe applied pressureoperating my atomizer assembly is also maintainedon the surface of the solution being atomized, no variation in theobserved light intensity results from a change'in hydrostatic head asthe sample is being consumed. Thus, another of the undesirable featuresobserved in the prior type'sof atomizers is avoided. 1 Since thedelivery end of the liquid tube 25 need not be less than 0.5 mm. indiameter, samples containing an appreciable" amount of suspendedmaterial will pass through the tube without serious interruption of theatomizers action. Human serum diluted 1:1 may be atomized withoutdifiiculty. Moreover, the vapor path from the atomizer jet to the burnermay be as little as approximately the order of 3 inches and hence thedifliculties and erratic behavior observed in atomizer assembliesembodying relatively long and complicated vapor paths are minimized, ifnot overcome.

Another outstanding feature of the invention is the high'sensitivity andoperating stability achieved with a low rate of sample consumption whichis of the order of 4 to 6 ml. per hour, as compared to approximately 23ml, per minute in other types of'atomizing units. This feature isattributable to the continuous return of the bulk of the sample to thesample container. In other words, only so much of the sample as istransformed into a fine mist passes into the burner, the relativelyheavy droplets and'condensate being returned to the container bygravity.

Another feature of the invention is the ease of removing contaminationdue to the preceding sample. Ordinarily two distilled Water flushings ofa few seconds duration is adequate to rinse the atomizer assemblysatisfactorily after-normal uses; but in event fairly concentratedsolutions are tested, such as those having a solids content of 1,000 p.p. m. or greater, an additional rinse may be required, but in no casehas any difficulty or serious delay been encountered in cleaning out theassembly.

Since, as above noted, relatively low air or oxygen pressure is requiredthere is a corresponding reduction both in the amount of air or oxygenused and the amount of combustible gas, and over a period of time theresultant saving is appreciable.

. While I have shown and described one desirable embodimentof theinvention, it is to be understood that this disclosure is for thepurpose of illustration and that various changes and modifications maybe made without departing from the spirit and scope of the invention asset forth in the appended claims.

I claim:

'1. In a flamespectrophotometer of the type having a light=slit andburner aligned therewith, the burner havinga fuel inlet and an inlet forthe atomized sample, an atomizer assembly disposed below said burner andcomprising an atomizing' chamber, the lower part of which receives thesample to be tested and the upper part of said chamber being ofgenerally conical shape and de fining a restricted outlet, aliquid-conveying tube having its lower end so positioned with respect tothe bottom of said atomizing chamber asto receive said. sample and itsdelivery end spaced below said restricted outlet, a pressure tubeextending into said atomizing chamber with its inner end contiguous tothe delivery end of said liquidconveying tube to provide an atomizerarranged to direct a spray upwardly toward said restricted outlet, areflux chamber having an inverted generally conical shaped lowerendportion defining an inlet communicating directly with said restrictedoutlet, :theupp'er part of said -eflux chamber having a delivery tubecommunicating with the inlet for the atomized sample, and'a bafilespaced above said restricted inlet sons to definewith the conical wallof said reflux chamber an annular shaped passage through which thespray'passes into the body of the chamber above said inlet, said baflleand lower part of said reflux chamber being so constructed and arrangedthat condensate and entrained droplets of said sample return bygravity'to said atomizing chamber.

2. In a flame spectrophotometer of the type having a light slit andburner aligned therewith, the burner'having a fuel inlet and an inletfor the atomized sample, an atomizer assembly disposed below said burnerand comprising an atomizing chamber, the lower part of which receivesthe sample to be tested and the upper part of said chamber being ofgenerally conical shape and defining a restricted outlet, aliquid-conveying tube having its lower end so positioned with respect tothe bottom of said atomizing chamber as to receive said sample and itsdelivery end spaced below said restricted outlet, a pressure tubeextending into said a-tomizing chamber with its inner end contiguous tothe delivery end of said liquidconveying tube to provide anatomizer'arranged to direct a spray upwardly toward said restrictedoutlet, areflux chamber having an inverted generally conical shapedlower end portion defining an inlet communicating directly with saidrestricted outlet, the upper end of said reflux chamber having aremovable closure formed with an out-let opening, a delivery tubeconnecting said outlet opening with the inlet for the atomized sample,and a battle spaced above the first mentioned inlet so as to define withthe conical wall of said reflux chamber an annular shaped passagethrough which the spray passes into the body of the chamber above saidinlet, said battle and lower part of said reflux chamber being soconstructed and arranged that condensate and entrained droplets ofsaidsample return by gravity to said atomizing chamber.

3. Apparatus as set forth in claim 1, wherein the lower end of saidatomizing chamber is opened and a loosely fitting cup-like containerdisposed about its lower wall portion to providea holder for saidsample.

4. Apparatus as 'set forth in claim 2, wherein said' baffle is supportedby said closure and consists of 'a concavoconvex member with its concavesurface facing said inlet.

References Cited in the =file of this patent UNITED STATES PATENTS1,839,193 Blanchard Jan. -5, 1932 2,532,687 Weichselbaum Dec. 5, 1950FOREIGN PATENTS 535,478 Germany Oct. 10, 1931 679,452 Germany Aug. v5,1939 640,808 Great Britain July 26,1950

